This invention relates in general to hybrid drive systems for vehicles and other devices having rotatably driven mechanisms. In particular, this invention relates to a brake interface circuit that can (1) selectively disable standard brakes provided for retarding the rotation of the rotatably driven mechanism and thereby allow the hybrid drive system to recover a maximum amount of energy during braking of the rotatably driven mechanism and (2) thereafter reliably re-enable the standard brakes for retarding the rotation of the rotatably driven mechanism when needed.
Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source of rotational power to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine generates rotational power, and such rotational power is transferred from an output shaft of the engine through a driveshaft to an input shaft of an axle so as to rotatably drive the wheels of the vehicle.
In some vehicles and other mechanisms, a hybrid drive system is provided in conjunction with the drive train system for accumulating energy during braking of the rotatably driven mechanism and for using such accumulated energy to assist in subsequently rotatably driving the rotatably driven mechanism. To accomplish this, a typical hybrid drive system includes an energy storage device and a reversible energy transfer machine. The reversible energy transfer machine communicates with the energy storage device and is mechanically coupled to a portion of the drive train system. Typically, the hybrid drive system can be operated in either a retarding mode, a neutral mode, or a driving mode. In the retarding mode, the reversible energy transfer machine of the hybrid drive system accumulates energy by braking or otherwise retarding the rotatably driven mechanism of the drive train system and stores such energy in the energy storage device. In the neutral mode, the hydraulic drive system is disconnected from the drive train system and, therefore, is substantially inoperative to exert any significant driving or retarding influence on the rotatably driven mechanism. In the driving mode, the reversible energy transfer machine of the hybrid drive system supplies the accumulated energy previously stored in the energy storage device to assist in subsequently rotatably driving the rotatably driven mechanism.
One commonly known hybrid drive system uses pressurized fluid as the actuating mechanism. In such a hydraulic hybrid drive system, a fluid energy storage device (such as an accumulator) and a reversible hydraulic machine are provided. Another commonly known hybrid drive system uses electricity as the actuating mechanism. In such an electric hybrid drive system, an electrical energy storage device (such as a battery) and a reversible electric machine are provided. Other hybrid drive systems are known in the art that use other actuating mechanisms. Regardless of the specific actuating mechanism that is used, the hybrid drive system can improve the performance of the drive train system (such as fuel economy, for example) by recovering and storing energy during deceleration and by retrieving and supplying the stored energy for use during a subsequent acceleration.
Although hybrid drive systems of this general type function in an energy-efficient manner, it is often necessary or desirable to provide a separate brake system to affirmatively slow or stop the rotation of the rotatably driven mechanism in certain situations. For example, when used in conjunction with the drive train system of a vehicle that is relatively heavy or moving relatively fast, the hybrid drive system may not always have the capacity to adequately retard the rotation of the rotatably driven mechanism as quickly as requested by a driver. Additionally, when used in conjunction with the drive train system of a vehicle that is stopped on an inclined surface, the hybrid drive system cannot positively stop the rotatably driven mechanism to prevent any movement of the vehicle. To address these and other situations, the separate brake system (which can be embodied as a conventional pneumatically or hydraulically actuated friction brake system) is often provided in conjunction with the hybrid drive system. In such a combined hybrid drive and brake system, the hybrid drive system can be actuated to normally retard the rotation of the rotatably driven mechanism in the energy-efficient manner described above, and the brake system can be actuated when otherwise necessary.
In a combined hybrid drive and brake system such as described above, deceleration of the rotatably driven mechanism can be accomplished by either (1) the brake system operating alone, (2) the hybrid drive system operating alone, or (3) both the brake system and the hybrid drive system operating in combination. The selection of which of these three operating modes is appropriate can be determined by a control apparatus in accordance with a variety of parameters. However, as mentioned above, the hybrid drive system alone may not always be able adequately retard or prevent the rotation of the rotatably driven mechanism when requested by a driver. Thus, it would be desirable to provide a brake interface circuit that can (1) selectively disable such standard brakes to allow the hybrid drive system to recover a maximum amount of energy during braking of the rotatably driven mechanism and (2) thereafter reliably re-enable the standard brakes for retarding the rotation of the rotatably driven mechanism when needed.